Telematics units are known and may be used to track and monitor vehicles such as cars, motorcycles, vans and trucks. The telematics unit is mounted in the vehicle and gathers information about the status of the vehicle. The telematics unit may then store the information for later retrieval, and/or report the information to a remote monitoring station using a mobile communications network.
An exemplary telematics unit may contain a Global Positioning System (GPS) unit, an accelerometer, a connection to a vehicle network (such as a Controller-Area Network or CAN) and a connection to a user interface. The GPS unit provides speed and position data, the accelerometer provides data indicating the acceleration of the vehicle (typically in three dimensions), the connection to the vehicle network provides a means for obtaining engine status, speed and fault data from the electronic control units (ECUs) of the vehicle, and the user interface enables interaction with the driver of the vehicle. The telematics unit can also contain a mobile communications transceiver which communicates with a controlling station and may send data to and receive data from the controlling station.
In general vehicles will carry loads of varying mass. The mass (or equivalently weight) of the load of the vehicle will affect the total mass of the vehicle—the total mass being derived from the sum of the unloaded or “kerb” weight of the vehicle and the weight of the load of the vehicle (it will be understood that in the context of this document, mass and weight may be used interchangeably). This is particularly evident in goods vehicles, where the variable mass of a load may be significantly greater than the kerb weight of the vehicle; however, even in passenger vehicles, such as cars, busses and coaches, the mass of the load may account for a significant fraction (>20%) of the total mass.
Accurate knowledge of the mass of a vehicle (or equivalently the mass of the load of the vehicle) is important for a number of reasons. These include (but are not limited to):                a. being able to efficiently route a vehicle to take into account weight restrictions (on e.g. bridges), and to find the most fuel efficient route (an unladen vehicle may be more efficient over a shorter route with large inclines, while an equivalent vehicle carrying a heavy load may be more efficient over a longer but flatter route);        b. being able to account for vehicle weight/mass when determining driver efficiency—companies employing professional drivers (i.e. haulage companies) often compare the fuel consumed by drivers so as to promote fuel efficient driving; since the fuel consumption of a vehicle increases as the weight of the vehicle increases, a measure of vehicle weight is important to enable accurate comparisons between drivers;        c. being able to estimate the wear on a vehicle. A heavy load will increase the amount of wear on a vehicle, therefore by recording the weight of the vehicle, a more accurate estimate of wear can be made, and therefore the service intervals of the vehicle can be properly assessed.        
One known method of measuring the weight of a vehicle is to use a “weighbridge” of “truck-scale” which is, in effect, a large set of scales which weighs the whole vehicle. The problems with using a weighbridge are the cost of the equipment, and that it is not practical to weigh a vehicle often, since the vehicle needs to travel to the weighbridge to be weighed.
Other methods of measuring vehicle weight involve measuring the downward force on the wheels. This may be done by measuring the displacement of the suspension, or changes in tyre pressure. The problem with such systems is that it requires additional equipment (i.e. the sensors) to be installed in the vehicle, adding to the cost and complexity of the system.
Several parts and components of these embodiments of the present technology appear in more than one Figure; for the sake of clarity the same reference numeral will be used to refer to the same part and component in all of the Figures.